LEDs are becoming increasingly popular as a light source in decorative and Christmas lights due to their reliability, energy savings, longevity, and cool operation. Manufacturers of decorative light strings are constantly working to maximize the brightness and benefits of LEDs as a light source as well as reduce production cost to narrow the gap between traditional, incandescent and LED light string cost.
It is known in the art the use of a DC power supply to power LED lamps maximize LED brightness and longevity. However, prior art discloses the use of a full bridge rectification circuit that requires additional conductor wires, separate enclosures to house rectifying diodes and/or additional conductor connections and/or voltage and current reducing devices, and places undue current load on rectifying diodes, detracting from the appearance of the light string and creating a potential safety hazard.
FIG. 1 shows a prior art embodiment of an LED light string comprising a light string requiring 4 conductor wires when a single series block of LED lamps and an end connector is employed. Five (5) conductor wires are required when two or more series blocks of LED lamps are employed. Both the AC to DC converter and additional wires imposed by this design add significant cost and detract from the aesthetics of the light string.
FIGS. 2A and 2B also show prior art embodiments of LED light strings. The prominent feature of these prior arts is circuit rectification wherein the rectifying diodes are installed in split pairs in an attempt to save wire, thus reducing cost. However according to the embodiment of FIG. 2A of the invention, three (3) conductor wires and a “dummy plug” is required when the light string does not have an end connector. In addition, significant modifications, enlarging the plug and/or end connector would be required in order to house the split pairs of rectifying diodes and voltage reducing devices. Alternately, the split diode pairs and voltage reducing devices would require a fairly large, separate enclosure to house them. Both of these options add significant cost and detract from the aesthetics of the light string.
According to the embodiment of FIG. 2B of this invention the number of conductor wires required in the manufacture of the light chain increases one-for-one with each parallel connected series block of LEDs added to the lighting chain. Thus, a light string employing 2 series blocks of LED lamps requires 4 conductor wires (3 series blocks require 5 conductor wires, etc.). An even larger enclosure is required in order to house the diode pairs, multiple conductor wires, and voltage reducing devices; Thus the invention disclosed defeats the wire saving purpose, adds cost, places severe limitations on the design, complicates the manufacturing process, and further detracts from the aesthetics of the light string.
In addition, both of the light string designs shown in FIG. 1 and FIGS. 2A and 2B create a safety hazard when additional series blocks of LED lamps are employed. The AC to DC converter (rectifying diodes) will quickly overheat due to the increased electrical load (current summation) imposed by the additional parallel connected series blocks of LED lamps. Accordingly, both of these designs have severe limitations.